Genome relation by Dot Plot (Gepard software)
M. ulcerans strains are characterized by the presence of a large, circular virulence plasmid called pMUM001 .
This plasmid harbours three large genes (mlsA1, mlsA2 and mlsB), encoding polyketide synthases that are required for the synthesis of the lipid toxin mycolactone that is the primary virulence factor for this pathogen.
pMUM001
Comparisons of multiple plasmid and chromosomal genes amongst ten M. ulcerans clinical isolates of diverse origins have suggested that plasmid acquisition was probably the key event that marked and permitted the recent emergence of M. ulcerans from a common Mycobacterium marinum progenitor.
M. ulcerans has undergone extensive gene loss due to DNA deletions, DNA rearrangements and pseudogene formation. Many of these changes have been mediated by some of the 213 copies of IS2404 and 91 copies of IS2606 .Neither of these insertion sequence elements (ISE) is present in M. marinum.
M. ulcerans and M. marinum are closely related to each other, as judged by 16S rRNA analysis, lipid profiles, and sequence comparisons of housekeeping and structural genes.
Despite their similarities, these two species have important phenotypic differences.
First, M. marinum grows relatively rapidly with a generation time of~ 4 h, where generation time of M. ulcerans and the M. tuberculosis-complex organisms is >20 h.
Second, similar to other pathogenic mycobacteria, M. marinum can live within host macrophages , whereas
M. ulcerans, which produces large ulcers, is possibly the only pathogenic Mycobacterium species that does not have a significant intracellular existence because it grows extracellularly.